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SSC Quantitative Aptitude Number System and its Operations Question Bank Numbers and Their Principles (I)

  • question_answer
    Twenty one times of a positive number is less than its square by 100. The value of the positive Number is          [SSC CGL Tier II, 2017]

    A) 25

    B) 26

    C) 42

    D) 41

    Correct Answer: A

    Solution :

    [a] Let, positive number \[=x\]
    According to the question,
                \[x\times 21={{x}^{2}}-100\]
    \[\Rightarrow \]   \[{{x}^{2}}-21x-100=0\]
    \[\Rightarrow \]   \[{{x}^{2}}-25x+4x-100=0\]
    \[\Rightarrow \]   \[x\,\,(x-25)+4\,\,(x-25)=0\]
    \[\Rightarrow \]   \[(x-25)(x+4)=0\]
    \[\Rightarrow \] \[x=25,\]\[-\,\,4\]
    Since number is positive
    \[\therefore \]      \[x=25\]


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